Not since Khruschev denounced Stalin at the 20th Communist party conference has there been a reforming speech like this. Pope Francis's interview with a fellow Jesuit journalist is one of the most sensational interviews of my lifetime. It amounts to a wholesale repudiation of the policies and priorities of the last two popes. The headline-grabbing stuff is all about sex, since that's what headlines always grab, but the real dynamite is elsewhere. There is actually very little any pope can do to control the sex lives of his followers and even of his priests. What will make a difference, and what he can control, is the internal government of the church, and the sense of purpose that he offers the clergy.

And right from the beginning of his interview it is clear that he has turned his back on the fortress Catholicism of the last two popes: he quotes St Ignatius, the founder of the Jesuits, as saying that "Great principles must be embodied in the circumstances of place, time and people."

Later, he adds that:

"The complaints of today about how 'barbaric' the world is – these complaints sometimes end up giving birth within the church to desires to establish order in the sense of pure conservation, as a defence. No: God is to be encountered in the world of today. If the Christian is a restorationist, a legalist, if he wants everything clear and safe, then he will find nothing."

It is impossible to read this except as a criticism of his predecessor Benedict XVI, who once said the European civilisation reached its height in the 14th century.

He urges a humane attitude to church discipline: he is himself sinner, he remembers.

"In life, God accompanies persons, and we must accompany them, starting from their situation. It is necessary to accompany them with mercy. When that happens, the holy spirit inspires the priest to say the right thing.
This is also the great benefit of confession as a sacrament: evaluating case by case and discerning what is the best thing to do for a person who seeks God and grace. The confessional is not a torture chamber, but the place in which the Lord's mercy motivates us to do better."

None of this would work if it were only imposed from above. But what he has done here is to make it impossible for reactionary bishops to demand that their priests clamp down on sexual sin among the congregation. The official teaching on sexuality is so wildly out of kilter with what most faithful Catholics believe and do, and so much felt to be contrary to what their consciences tell them, that he is pushing at an open door here. The parish priests are now freed to act as their consciences tell them.

The defeat of the church's conservatives is utterly comprehensive in this interview. All of their favourite causes are taken up and rejected – "It is not necessary to talk about … abortion, gay marriage and [contraception] all the time" says the pope. So much for the "culture of death" that Pope John Paul II thought he saw in those things: "The church's pastoral ministry cannot be obsessed with the transmission of a disjointed multitude of doctrines to be imposed insistently."

Then the favourite trick (not least in England) of reactionaries complaining to Rome about their own suspiciously liberal bishops is pilloried.

"It is amazing to see the denunciations for lack of orthodoxy that come to Rome. I think the cases should be investigated by the local bishops' conferences, which can get valuable assistance from Rome. These cases, in fact, are much better dealt with locally."

Then he wants a greater role for bishops in church governance, overturning 50 years of attempted centralisation. He rebukes liturgical traditionalists, who want to return to the Latin mass. They can have "this sensitivity" respected, but the formation of cliques around the old liturgy is explicitly denounced. This leaves no future for another of his predecessors' favourite policies: a reunion with the Lefevrist sect which rejected the Second Vatican Council.

So, there is a programme of decentralisation, of hope, and above all of realism and truth to experience. "When does a formulation of thought cease to be valid," asks Francis, and answers: "When it loses sight of the human or even when it is afraid of the human or deluded about itself." You cannot imagine his predecessors saying this. I can just about imagine his bishops, now, hearing it.